How to fix internal server error in minecraft

How to fix internal server error in Minecraft:
___________________________________________________________________________________________________________ 1.Contact your server owner in some way unless your the owner.

2. Tell him to delete your player data and beg him to copy his permissions, and delete them and put them back on.

3.It could be essentials. So tell the owner to delete essentials and re-install them.

I hope this worked this has worked for several of my friends and I